The present invention relates to an overload release clutch which transmits rotary movement of a driving member to a driven member and which serves to prevent application of torque beyond a predetermined limit.
An overload release clutch of this kind is known and disclosed, for example, in Japanese Patent Publication No. 30524/80. This known overload release clutch includes a pair of cylindrical hollow sleeves overlapping with each other, one of which is fixed on the outer periphery of a drive shaft and the other is on a driven shaft. A plurality of arcuate recesses are formed on the outer surface of the inner sleeve along the circumferential direction thereof and each extends in the axial direction thereof, while corresponding grooves are provided on the inner surface of the outer sleeve. A ball member made of steel or the like is disposed between each recess and groove and is pressed against the bottom surface of the recess by means of a compression spring, so that the inner and outer sleeves are coupled with each other. When a torque load beyond a predetermined limit, which is set by adjusting compression force of the spring, is applied between the drive and driven shafts, the balls are caused to roll out of the recesses against the compression force to thereby release the engagement between the drive and driven shafts.
However, since this overload release clutch transmits rotary movement through point contacts between the balls and the bottom surfaces of the recesses particularly in the axial direction of the sleeves, the pressure of the contact portion becomes so high that deformation may arise on the contact portion, which results in malfunction or short service life of the device. Prevention of the deformation requires lessening of the pressure on the contact portion by increasing the contact area; however, very high precision is required if the bottom surface of the recess should be formed to have the same curvature as the ball, which is impractical.